1. Technical Field
The present invention generally relates to fluid stop valves, and more particularly to a butterfly valve that can effectively operate across a wide range of temperatures including cryogenic temperatures.
2. Description of the Related Art
A generally-known butterfly valve is a valve which can be used for isolating or regulating flow. The closing mechanism takes the form of a disc. Operation is similar to that of a ball valve, which allows for quick shut off. Butterfly valves are generally favored because they are lower in cost to other valve designs as well as being lighter in weight, meaning less support is required. The disc is positioned in the center of the pipe. Passing through the disc is a rod connected to an actuator on the outside of the valve. Rotating the actuator turns the disc either parallel or perpendicular to the flow. Unlike a ball valve, the disc is always present within the flow. Therefore a pressure drop is always induced in the flow, regardless of valve position. A butterfly valve is from a family of valves called quarter-turn valves. In operation, the valve is fully open or closed when the disc is rotated a quarter turn. The “butterfly” is a metal disc mounted on a rod. When the valve is closed, the disc is turned so that it completely blocks off the passageway. When the valve is fully open, the disc is rotated a quarter turn so that it allows an almost unrestricted passage of the fluid. The valve may also be opened incrementally to throttle flow.
The high flow rate and relatively low pressure drop at full flow are some of the advantages that butterfly valves have over other valves. Other advantages include simplicity of operation, compact valve body and relatively low cost. However, balanced against these advantages butterfly valves have high valve seat wear and inability to maintain a tight seal. Additionally, if the valve is used to throttle the fluid flow or to frequently cycle to open and closed positions, these disadvantages are amplified and additionally frequent repair is required. Therefore a need exists for a butterfly valve with improved sealing characteristics, and in particular for cryogenic applications.